Surface characterization of red maple strands after hot water extraction
The conversion of carbohydrates from wood to make biofuels such as ethanol is a topic of widespread interest. A promising approach is the removal of the hemicellulosic wood component by extraction with subsequent conversion to biofuels while continuing to produce forest products. The impact of extraction on wood strands for use in strand-based composites was investigated. One tree of red maple (Acer rubrum L.) was used to create strands 10.2 cm long with a thickness of 0.9 mm. Three hot water extraction procedures at 160°C, corresponding to severity factors (SF) of 2.71, 3.54, and 3.81, were used resulting in an average weight loss of 5.7, 16.9 and 18.1%, respectively. Scanning electron microscopic imaging of selected wood strands showed that pores in the cell wall increased as SF increased. The distribution and size of the cell-wall pore structure showed up to a 22.2% increase. The sessile drop method, using distilled water, diiodomethane, and ethylene glycol, indicated more pronounced liquid wetting and penetration as SF increased. Inverse gas chromatography led to the finding that dispersive surface-free energy and acid-base characteristics increase with SF. The extraction procedures should be kept below a SF of 3.54 to minimize changes in adhesion performance.